In a display device using non-light emitting optical components, such as a liquid crystal display device, a backlight unit is provided behind a display panel such as a liquid crystal display panel for illuminating the display panel. Many backlight units of such a kind includes a plurality of elongated straight tube type lamps as light sources. Such backlight units generally include a plurality of the lamps and light emitted from the lamps is equalized by diffuser plates.
Due to a recent increasing demand for reductions in thickness and power consumption, problems to be solved for the backlight units are becoming clear. For example, the lamps and are closely arranged to diffuser plates to reduce the thickness of the backlight units. As a result, brightness becomes uneven or uneven luminance distribution may occur due to shadows of the lamps.
Patent Document 1 discloses a backlight unit as means for making luminance distribution uniform. It includes a reflector and a light transmissive diffuser plate that face each other via fluorescent lamps. The reflector has a band-like specular reflection section that mainly provides specular reflection in a part that is off the fluorescent lamps, that is, does not directly face the fluorescent lamps. The other part of the reflector is a diffuse reflection section that mainly provides diffuse reflection. According to the backlight unit, light rays specularly reflected off the specular reflection section converge at a middle point between the fluorescent lamps. Therefore, an decrease in brightness at that point is complemented and thus the luminance distribution becomes uniform.
Patent Document 2 discloses an apparatus including a plurality of straight tube lamps arranged substantially in parallel along longitudinal right and left sides of a display screen of a display panel. Moreover, they are arranged at a small interval in an area corresponding to a central area of the display screen of the display panel. The interval becomes larger with a constant pitch toward an upper end area and a lower end area of the display screen this arrangement may be referred to as an irregular lamp pitch). The apparatus is made focusing on a fact that human eyes tend to rest on around the center of screen and thus a light difference in brightness between edges and the center of the screen, that is, the edges is slightly darker than the center, is not noticeable. Based on that fact, the number of the lamps can be reduced while the uniformity of the luminance distribution is maintained. This produces power saving effects.    Patent Document 1: Japanese Unexamined Patent Publication No. 2004-354533    Patent Document 2: Japanese Patent Publication No. 3642723
(Problem to be Solved by the Invention)
The above documents, however, do not disclose adequate solutions for making the luminance distribution uniform in large screen liquid crystal display devices. Thus, farther technology development is urgently needed. Especially, the irregular lamp pitch disclosed in Patent Document 2 may experience uneven brightness or display unevenness because a correlation between the lamp arrangement and the overall screen brightness is very sensitive. At the edges of the screen, the amount of light is not sufficient because the interval between the lamps is large resulting in the brightness unevenness, or the light is not sufficiently reflected and shadows of the lamps may appear on the screen resulting in the display unevenness.